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With the success of the impact-echo method in determining the
depth of surfaceopening cracks in slab-like structures or large
members in which boundaries have minor effets on stress wave
propagation, the study of this thesis aims at extendingthe
application of stress wave progation technique to measure the
depths of surface-opening cracks in reinforced concrete beams
commonly used in bridge structures. Experimental studies were
carried out on full-scale reinforced concrete beams in order to
realize the effects caused by close boundaries, and futhermore,
to understand the disturbances in recorded displacement
waveforms caused by the presence of steel bars. Numerical
studies were also performed tocomplement the experiments. The
recorded displacement waveform were analyzed primarily in the
time domain. Finally, all the actual depth of surface-opening
cracks were identified both by dyeing and coring. The results
obtained from thethese studies show that the modified impact-
echo method based on time domain analysis can accurately measure
the depths of cracks in spite of the close boundariesand the
presence of steel bars. Together with frequency domain analysis
of the recorded waveforms, flexureshear inclined cracks can also
be evaluated. Therefore, the modified impact-echo method is
highly feasible to evaluate the depths of surface-opening carcks
in real reinforced concrete structures.
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